1. Field of the Invention
This invention relates to a method of and a system for conveying a sheet to be scanned to an arcuate concave surface of a sheet holding device, such a sheet holding device, and a method of holding the sheet.
2. Description of the Related Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, xcex1-rays, xcex2-rays, xcex3-rays, cathode rays or ultraviolet rays, they store a part of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is generally referred to as xe2x80x9ca stimulable phosphorxe2x80x9d. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as xe2x80x9cstimulated emissionxe2x80x9d. There has been known a radiation image recording and reproducing system in which a sheet provided with a layer of the stimulable phosphor (will be referred to as xe2x80x9ca stimulable phosphor sheetxe2x80x9d, hereinbelow) is first exposed to a radiation passing through an object to have a radiation image of the object stored on the stimulable phosphor sheet, a stimulating light beam such as a laser beam is caused to scan the stimulable phosphor sheet so that the stimulable phosphor sheet emits stimulated emission as signal light bearing thereon information on the radiation image, the stimulated emission is photoelectrically detected, thereby obtaining an image signal (a radiation image signal), and the radiation image of the object is reproduced as a visible image on the basis of the image signal on a recording medium such as a photographic film or a display such as a CRT. See, for instance, Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)11395 and 56(1981)-11397, and Japanese Patent Publication No. 1(1989)-60784.
There has been known an autoradiography using the principle of the radiation image recording and reproducing system in which an organism such as a rat is administered with a radioactive marker substance, a sample of a tissue of the organism is kept on the stimulable phosphor layer of the stimulable phosphor sheet for a predetermined time to have the stimulable phosphor absorb radiation energy radiated from the sample, a stimulating light beam is caused to scan the stimulable phosphor sheet so that the stimulable phosphor sheet emits stimulated emission, the stimulated emission is photoelectrically detected to form a digital image signal, a predetermined signal processing is carried out on the digital image signal, and a visible image is reproduced on the basis of the processed digital image signal on a recording medium such as a photographic film or a display such as a CRT, thereby obtaining information on the distribution of the radioactive marker substance in the sample. See, for instance, Japanese Patent Publication Nos. 1(1989)-60784, 1(1989)-60782 and 4(1992)-3952.
Further, there has been proposed a chemiluminescence detecting system in which a high polymer fixed with its protein sequence, nucleic acid sequence and the like is selectively labeled with a marker substance which causes a chemiluminescence substance to emit chemiluminescence upon contact therewith, the high polymer selectively labeled with the marker substance is brought into contact with a chemiluminescence substance, the stimulable phosphor of the stimulable phosphor sheet is caused to store the energy of the chemiluminescence in a visible wavelength range emitted upon contact of the marker substance with the chemiluminescence substance, an electromagnetic beam is caused to scan the stimulable phosphor sheet so that the stimulable phosphor sheet emits stimulated emission, the stimulated emission is photoelectrically detected to form a digital image signal, a predetermined signal processing is carried out on the digital image signal, and a visible image is reproduced on the basis of the processed digital image signal on a recording medium such as a photographic film or a display such as a CRT, thereby obtaining information on the high polymer such as genetic information. See, for instance, Japanese Unexamined Patent Publication Nos. 3(1991)-205550 and 4(1992)-232864.
These systems includes an image read-out apparatus having a stimulating beam scanning device for scanning the stimulable phosphor sheet with a stimulating beam or the like. The stimulating beam scanning device generally comprises, as shown in FIG. 2A, a sheet holding device 20 which holds a stimulable phosphor sheet 10 on a sheet holding surface 23a, which is an arcuate concave surface, and is movable in the direction of arrow Y parallel to the generatrix of the sheet holding surface 23a, a stimulating light source 40, a photoelectric conversion means 50 such as a photomultiplier which outputs an electric signal S according to the amount of light received and a spinner (a main scanning means) 30 which is rotated in the direction of arrow X by an electric motor (not shown) about a central axis Y0 of curvature of the arcuate sheet holding surface 23a while projecting a beam L of stimulating light emitted from the stimulating light source 40 onto the stimulable phosphor sheet 10 held on the sheet holding surface 23a through a lens 31 provided on a part of its peripheral wall, collecting stimulated emission M emitted from the stimulable phosphor sheet 10 upon stimulation by the stimulating light beam L, and causing the collected stimulated emission M to impinge upon the photoelectric conversion means 50.
As shown in more detail in FIG. 2B, the spinner 30 is provided therein a mirror 32 which reflects the stimulating light beam L, which is emitted from the stimulating light source 40 and reflected by a mirror 41 and a dichroic mirror 42 to enter the spinner 30 along the central axis Y0, toward a condenser lens 31 provided on the peripheral surface of the spinner 30. The mirror 32 also reflects the stimulated emission M, which is emitted from the stimulable phosphor sheet 10 and collected by the condenser lens 31, toward the photoelectric conversion means 50 along the central axis Y0.
Conventionally, the stimulable phosphor sheet 10 is conveyed to the sheet holding surface 23a of the sheet holding device 20 of the image read-out apparatus, for instance, by a sheet conveying system shown in FIGS. 4A and 4B which are views as seen in the direction of arrow A in FIG. 2A.
The sheet conveying system shown in FIGS. 4A and 4B comprises conveyor rollers 21 and 22 which convey the stimulable phosphor sheet 10 along the sheet holding surface 23a in the circumferential direction, a leading end detecting means which is formed by a lever 24 urged by a spring 24a and a sensor 26 and detects that the leading end 10a of the stimulable phosphor sheet 10 reaches a predetermined position where it abuts against a stopper 23b, and a sheet positioning means 25 which positions the stimulable phosphor sheet 10 in place on the sheet holding surface 23a by positioning the trailing end 10b of the stimulable phosphor sheet 10 in response to detection of the leading end 10a by the leading end detecting means. That is, when the leading end 10b of the stimulable phosphor sheet 10 is brought into abutment against one end portion of the lever 24 and moves upward the lever 24 overcoming the force of the spring 24a, the lever 24 is rotated in the clockwise direction to the stopper 23b as shown in FIG. 4B. The sensor 26 is normally detecting the distance to the other end portion of the lever 24 and the sensor 26 detects that the leading end 10a of the stimulable phosphor sheet 10 reaches the stopper 23 through the distance to the other end portion of the lever 24. Then the sensor 26 informs a control means 27 of the fact that it has detected that the leading end 10a of the stimulable phosphor sheet 10 reaches the stopper 23, and, upon receipt of the information, the control means 27 stops the conveyor rollers 21 and 22 and rotates the trailing end positioning means 25 to push the trailing end 10b of the stimulable phosphor sheet 10 and position the trailing end 10b as shown in FIG. 4B.
After the leading end 10a and the trailing end 10b of the stimulable phosphor sheet 10 are thus positioned, the stimulable phosphor sheet 10 is sucked against the sheet holding surface 23a through a plurality of suction holes 23c formed in the sheet holding surface 23a and thus held on the sheet holding device 20 and then the conveyor rollers 21 and 22 are retracted from the sheet holding surface 23a. In this state, the image on the stimulable phosphor sheet 10 is read out by operating the spinner 30.
In such a sheet conveying system, there has been a problem that the sheet driving force is reduced by dynamic friction acting between the sheet holding surface 23a and the surface of the stimulable phosphor sheet. Since the dynamic friction increases as the contact area between the sheet holding surface 23a and the stimulable phosphor sheet 10 increases, the sheet driving force required to convey the stimulable phosphor sheet 10 along the sheet holding surface 23a is increased as the size of the stimulable phosphor sheet 10 increases.
Further, in the sheet holding device, there has been a problem that, though the suction holes 23c should be as many as possible in order to stably and uniformly hold the sheet to be scanned on the sheet holding surface 23a, forming many suction holes 23a by machining is a labor-consuming process and adds to the manufacturing cost.
Further, in the sheet holding device, there has been also a problem that air is sometimes trapped between the stimulable phosphor sheet 10 and the sheet holding surface 23a between suction holes arranged in the circumferential direction of the sheet holding surface 23a. When air is trapped between the stimulable phosphor sheet 10 and the sheet holding surface 23a, the part of the stimulable phosphor sheet 10 can be held away from the sheet holding surface 23a, which results in fluctuation in distance between the surface of the stimulable phosphor sheet 10 and the spinner 30. The distance between the surface of the stimulable phosphor sheet 10 and the spinner 30 is reduced at the part where the stimulable phosphor sheet 10 is held away from the sheet holding surface 23a and the detected intensity of the stimulated emission M is unreasonably increased, whereby accuracy in reading the image is deteriorated.
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and a system for conveying a sheet to be scanned such as a stimulable phosphor sheet to and out of an arcuate and concave sheet holding surface which can convey the sheet to be scanned with a relatively small driving force.
Another object of the present invention is to provide a sheet holding device for holding a sheet to be scanned on an arcuate and concave sheet holding surface which can stably and uniformly hold the sheet on the sheet holding surface with a relatively small number of suction holes.
Still another object of the present invention is to provide a method of and a device for holding a sheet to be scanned on an arcuate and concave sheet holding surface which can hold the sheet in a close contact with the sheet holding surface over the entire area thereof without any part held away from the sheet holding surface.
In the method of and the system for conveying a sheet to be scanned in accordance with the present invention, the dynamic friction acting between the sheet holding surface and the surface of the stimulable phosphor sheet by blowing air or the like through an air blow hole formed in the sheet holding surface so that an air layer is formed at least a part of the interface between the sheet and the sheet holding surface and the contact area between the sheet and the sheet holding surface is reduced when the sheet is to be conveyed to or out of the sheet holding surface.
That is, in accordance with a first aspect of the present invention, there is provided a method of conveying a sheet to be scanned to a sheet holding device provided with a support member having an arcuate and concave sheet holding surface and a sheet holding means for holding the sheet on the sheet holding surface in which the sheet is conveyed along the sheet holding surface in a circumferential direction thereof and is positioned in a predetermined position on the sheet holding surface, wherein the improvement comprises the step of,
blowing gas between the sheet holding surface and the sheet when the sheet is conveyed to and out of the sheet holding device through a gas blow hole formed in the sheet holding surface.
Generally the arcuate and concave sheet holding surface is a part of the inner surface of a cylinder. For example, the sheet may be conveyed by the use of conveyor rollers. Further, the sheet holding means may comprise, for instance, a magnetic means which magnetically holds the sheet on the sheet holding surface or a suction means which holds the sheet on the sheet holding surface under vacuum supplied through a plurality of suction holes formed in the sheet holding surface.
It is preferred that the sheet conveying means such as conveyer rollers be provided not only in a position from which the sheet is conveyed in the sheet holding surface (will be referred to as xe2x80x9cthe sheet-in positionxe2x80x9d, hereinbelow) but also in a position between the sheet-in position and a position where the leading end of the sheet is finally positioned (will be referred to as xe2x80x9cthe leading end holding positionxe2x80x9d, hereinbelow), whereby the sheet driving force is enhanced and the sheet can be conveyed in and out of the sheet holding device more smoothly coupled with the effect of the gas blown between the sheet holding surface and the sheet. Especially, this is useful in the case of a read-out apparatus where a sheet longer than the conventional sheet in a length in the direction of conveyance is used and accordingly the dynamic friction acting between the sheet and the sheet holding surface is larger.
In accordance with a second aspect of the present invention, there is provided a system for carrying out the method in accordance with the first aspect of the present invention, that is, a system for conveying a sheet to be scanned to a sheet holding device provided with a support member having an arcuate and concave sheet holding surface and a sheet holding means for holding the sheet on the sheet holding surface, the system comprising conveyor means for conveying the sheet along the sheet holding surface in a circumferential direction thereof and a positioning means for positioning the sheet in a predetermined position on the sheet holding surface, wherein the improvement comprises
a gas blow hole formed in the sheet holding surface and
a gas blow means which blows gas between the sheet holding surface and the sheet when the sheet is conveyed to and out of the sheet holding device through the gas blow hole.
In accordance with the first and second aspects of the present invention, a gas layer (typically an air layer) is formed between the sheet and the sheet holding surface and the friction between the sheet and the sheet holding surface is weakened, whereby the sheet can be conveyed with relatively small sheet driving force.
In accordance with a third aspect of the present invention, there is provided a sheet holding device comprising a support member having an arcuate and concave sheet holding surface provided with a suction hole and a suction means which supplies suction force through the suction hole to hold the sheet on the sheet holding surface under vacuum, wherein the improvement comprises that
at least one groove is formed in the sheet holding surface and the suction hole is formed in the groove.
The term xe2x80x9cgroovexe2x80x9d as used here need not be limited to express an elongated groove but should be broadly interpreted to express a recess larger than opening of the suction hole like a seat.
In the case where the sheet is conveyed along the sheet holding surface in a circumferential direction thereof, it is preferred that the groove has no outer edge extending in a direction perpendicular to the circumferential direction of the sheet holding surface. That is, when the sheet is conveyed in the sheet holding surface, the sheet is arcuately bent under normal drag from the arcuate sheet holding surface. However, since the sheet tends to be restored under its resiliency, there is fear that, when there is a groove having an outer edge extending in a direction perpendicular to the circumferential direction of the sheet holding surface, the leading end of the sheet can interfere with the wall of the groove to obstruct smooth conveyance of the sheet. For example, the groove may be X-shaped.
In accordance with the third aspect of the present invention, since suction force can be applied to the sheet through the opening of the groove, the sheet can be stably and uniformly sucked against the sheet holding surface through a relatively small number of suction holes.
In accordance with a fourth aspect of the present invention, there is provided a method of holding a sheet to be scanned, which is conveyed along an arcuate and concave sheet holding surface of a support member in a circumferential direction thereof from one edge of the sheet holding surface toward the other edge thereof, on the sheet holding surface under suction force applied to the sheet through a plurality of suction holes formed in the sheet holding surface, wherein the improvement comprises the steps of
forming a plurality of suction holes in different positions in the circumferential direction of the sheet holding surface between said one edge of the sheet holding surface and the other edge thereof and supplying suction force to the suction holes in sequence from the suction hole nearest to said the other edge of the sheet holding surface to the suction hole nearest to said one edge of the same.
Generally the arcuate and concave sheet holding surface is a part of the inner surface of a cylinder. For example, the sheet may be conveyed by the use of conveyor rollers. Further, suction force may be applied to the suction holes by, for instance, a suction pump.
In the case where the sheet is conveyed along the sheet holding surface with air blown between the sheet and the sheet holding surface, the method in accordance with the fourth aspect of the present invention is especially useful. In this case, an air layer is more apt to be trapped between the sheet and the sheet holding surface.
In accordance with a fifth aspect of the present invention, there is provided a device for holding a sheet to be scanned, which is conveyed along an arcuate and concave sheet holding surface of a support member in a circumferential direction thereof from one edge of the sheet holding surface toward the other edge thereof, on the sheet holding surface under suction force applied to the sheet through a plurality of suction holes formed in the sheet holding surface, wherein the improvement comprises
a plurality of suction holes formed in different positions in the circumferential direction of the sheet holding surface between said one edge of the sheet holding surface and the other edge thereof and
a suction means which supplies suction force to the suction holes in sequence from the suction hole nearest to said the other edge of the sheet holding surface to the suction hole nearest to said one edge of the same.
In accordance with the fourth and fifth aspects of the present invention, since the sheet is attracted to the sheet holding surface from the leading end thereof toward the trailing end thereof, air between the sheet and the sheet holding surface is gradually pushed toward the trailing end of the sheet and purged through the sides and/or the trailing edge of the sheet, whereby the sheet can be held in a close contact with the sheet holding surface over the entire area thereof without any part held away from the sheet holding surface.